Almost 40 percent of Arizona’s water supply comes from an ancient source — aquifers deep underground that collected water over millions of years.

Those aquifers aren’t considered a renewable source by water-policy experts given they formed during prehistoric times and are almost always sucked down more quickly than they’re refilled.

In several Arizona communities, that finite source of water is in danger of being overtapped. Water experts and environmentalists say that's why the state needs tighter groundwater restrictions.

But some power brokers in the Arizona Legislature want to do the opposite.

They have introduced bills that either sidestep the problem or seek to eliminate rules on aquifer pumping. One proposal would allow two rural counties to reverse laws that require new subdivisions have a 100-year water supply.

That has stoked concerns for both conservationists and Gov. Doug Ducey’s administration. Ducey vetoed two similar bills in 2016 and mightdo so again.

Still, opponents say the Legislature's push for deregulation is indicative of an unwillingness to protect aquifers.

Kathleen Ferris, a Phoenix water attorney and a former director of the Arizona Department of Water Resources, said thelawmakers' bills aim to move the state in the wrong direction, toward deregulation.

“It doesn’t do anything for groundwater management essentially, anything to improve it,” Ferris said of water-related bills. “And in many cases, they’re detrimental.”

Deregulation push at the Capitol

Water policy is one of the dominant issues at the state Capitol this legislative session. Ducey has called for broad reforms to ensure the state remains a steward of its groundwater and Colorado River water.

Rep. Rusty Bowers, R-Mesa, on House Bill 2512, which would let counties rescind the state's 100-year water supply rule

Two Republican state lawmakers, Sen. Gail Griffin of Hereford and Rep. Rusty Bowers of Mesa, have led the deregulation effort.

Griffin and Bowers have called their bills works in progress. Bowers said he hopes to balance conservation while supporting economic development because the water is for people to use, after all.

“We also have to have development and we have to have lives,” he said during a debate over the legislation.

The lawmakers have described their drive to let counties rescind the 100-year water supply rule — primarily Cochise County in southeastern Arizona — as a move to let local governments decide what’s best for themselves.

Aquifers in overdraft raise alarm

The push for deregulation comes as several areas of Arizona grapple with projections that they're running low on groundwater.

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Under state law, developers cannot build subdivisions in some areas of the state, including the Pinal County areaand Phoenix and Tucson areas, unless they can prove they have an 100-year water supply.

The state is recalculating its Pinal projections, citing concerns that the modeling might be too conservative. But it’s unclear how much water that could free up for homes. Everyone concedes there are more water rights on paper than there is water stored underground in Pinal County.

COCHISE COUNTY: Environmentalists and the federal government are fighting a developer’s plans to build Tribute, a subdivision that would bring about 7,000 homes to Sierra Vista. They’re battling in court.

Griffin and Bowers’ bill would allow the county to opt out of the 100-year water supply requirement for new subdivisions, which could allow the developer to build.

MOHAVE COUNTY: An aquifer that supplies water to residents of Kingman and farmers in the nearby Hualapai Valley could be depleted within 55 years, according to a study county officials have circulated.

Like other rural areas, Mohave County well owners can pump unlimited amounts of groundwater, and they can do it without reporting their water use to anyone. More than 160 new wells, some pumping for water-heavy crops like alfalfa, have sprung up in recent years.

County supervisors have urged state lawmakers to allow them to impose reporting requirements for large wells, so they know much is being drained. That bill hasn’t gained traction at the Capitol.

Lasting impacts of overpumping

If the state doesn’t take action, the consequences of inaction could be significant.

Scientists say excessive groundwater pumping can permanently damage water quality and shrink the size of aquifers.

According to the United States Geological Survey, the impacts of overpumping include:

LOWERING THE WATER TABLE: The water table is the point underground below which layers of porous rock and sediment are saturated with water. Excessive pumping causes the water table to drop.

That can force well users to drill deeper to get water, a costly endeavor. Eventually, how much water a well produces can decline. Aquifers can recharge themselves, but Mother Nature works slowly and the process can take hundreds or thousands of years.

Arizona has aquifer recharge programs, which pump treated wastewater and other excess supplies back into the ground. But recharge efforts rarely match what's getting pumped out of an aquifer.

DEWATERING RIVERS AND STREAMS: While state law generally treats groundwater and surface waters separately, hydrologists say they are closely interconnected. Rivers that run year-round receive a good portion of their flow from groundwater that seeps into the stream bed.

Groundwater pumping of a shared aquifer can effectively drain water from rivers, lakes and streams, as conservationists warn could harm the San Pedro River.

LAND SUBSIDENCE: As an aquifer is drained, the soil that was once saturated with water can collapse and compact. That literally causes the ground above it to sink. Historically, parts of south-central Arizona have sunk as much as 12.5 feet, according to USGS.

As land sinks, large cracks or fissures in the earth can form. Those fissures can damage utility lines, roads, canals and building foundations.

Push to cut rules along San Pedro River

Cochise County has been ground zero in the debate over this year’s proposed groundwater legislation.

Bowers and Griffin have pushed to allow the county to opt out of the 100-year water supply requirement, saying the local community knows how best to handle its water.

Under state law, developers in more populous areas must have a 100-year water supply for new subdivisions. The act doesn't apply to most of the state's rural counties, where builders can still sell homes on dry lots.

“There's few things that are more worthless than a house in the desert without water. This is truly putting our future on the line.”

Rep. Kirsten Engel, D-Tucson, one of the Legislature's most outspoken opponents of the Griffin-Bowers bill

But two rural counties, Cochise and Yuma, previously have voluntarily agreed to enact a version of the 100-year water requirement.

Now, Cochise officials have asked to lift the rule in light of the fight to stop construction of Tribute. Sierra Vista provides housing for many military families given its proximity to nearby Fort Huachuca.

Griffin, a real-estate broker who represents the area, said there is “abundant groundwater in the aquifer.” She said the county has some of the most aggressive water-savings programs in the state.

“It just allows the local government to make decisions for themselves,” Griffin said of the bill.

Ferris, who played a key role in writing the 1980 Groundwater Management Act that created the 100-year requirement, said Griffin’s claim that Cochise has plenty of water is simply untrue.

Those conditions lead conservationists to worry that large-scale development reliant on groundwater could harm the San Pedro River, a desert oasis that millions of migratory birds use. It hosts endangered species, including the western yellow-billed cuckoo and southwestern willow flycatcher.

As a national conservation area, the river has superior water rights and future homeowners could be cut off from the aquifer if a court finds the river is being harmed.

Rep. Kirsten Engel, D-Tucson, has been one of the Legislature's most outspoken opponents of the Griffin-Bowers bill. She said letting counties remove the 100-year rule would be a “step backwards.”

She said allowing subdivisions to be built without a guaranteed water supply is also a consumer-protection issue.

“There's few things that are more worthless than a house in the desert without water,” said Engel, an environmental attorney. “This is truly putting our future on the line."

Opposition has also come from some Republican lawmakers.

“This bill will cause businesses and industry to question the state’s commitment to water security,” said Rep. Noel Campbell, R-Prescott.

That proposal to let counties reverse the 100-year water supply rules is just one of many provision that Griffin and Bowers have included in two omnibus water bills: Senate Bill 1507 and House Bill 2512.

The controversial deregulation provision would require counties that adopted the 100-year water supply rule to re-evaluate the decision, giving them the option to back out.

Fairbank Day will take place March 12. The event includes docent-led walks to the old cemetery and other historic sites, live music, food and a full-scale reenactment of the Fairbank train robbery. City of Sierra Vista

Historic ranch buildings have been restored by Friends of the San Pedro River, a non-profit organization dedicated to the river's conservation. Hunkered in the shade of massive cottonwoods, the San Pedro House serves as visitor center, bookstore and educational hub. Roger Naylor/Special for the Republic

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While SB 1507 narrowly failed in the Senate, HB 2512 passed in the House.

And a standalone bill that only contains the provision to let some counties opt out of the 100-year water rule passed the Senate.

Ducey vetoed a similar bill pair of bills in 2016, saying, “I will not sign legislation that threatens Arizona’s water future.”

The governor hasn’t taken a public stance on the deregulation proposal facing lawmakers this year. Kirk Adams, Ducey's chief of staff, said the 2016 veto is "probably a pretty good indicator" of where he stands.

Conservationists want new rules requiring a 100-year water supply for all new subdivisions, including those in rural areas, but state lawmakers have been unwilling to touch the issue.

Another area state lawmakers are urged to make changes: monitoring for wells that pump water in rural, agricultural areas.

Currently, well owners can pump as much water as they want without reporting it to anyone.

Republican leaders from theKingman area, including Mohave County Supervisor Gary Watson, want the state to enact new rules that include reporting for owners of large wells (those pumping over 500 gallons per minute).

Some GOP state lawmakers adamantly oppose the idea of well metering: “It’s your well, your property, your business," Rep. David Cook, R-Globe, said during a public hearing.